Fourdrinier wire drive mechanism and method



July 18: 1961 L. HoRNBosTEL ETAL 2,992,965

FOURDRINIER WIRE DRIVE MECHANISM AND METHOD Filed Jan. l1, 1960 5 Sheets-Sheet 1 d gafr I Just-gs July 18, 1961 L. HoRNBosTEL ETAL 2,992,965

FOURDRINIER WIRE DRIVE MECHANISM AND METHOD Filed Jan. ll, 1960 5 Sheets-Sheet 2 D j@ @W @W @M/ &5.

July 18, 1961 L. HoRNBosTEL ETAL 2,992,965

FOURDRINIER WIRE DRIVE MECHANISM AND METHOD Filed Jan. 1l, 1960 3 Sheets-Sheet 3 Unite it 2,992,965 FOURDRINIER WIRE DRIVE MECHANISM` AND METHOD Lloyd Hornbostel, Edward D. Beachler, and Edgar J, Justus, Beloit, Wis., assignors to Beloit Iron. Works,

Beloit, Wis., a corporation of Wisconsin Filed Jan. 11, 1960, Ser. No.,1,74`3 25 Claims. (Cl. 162-199) The instant invention relates to Fourdrinier type paper making machines, and more particularly, toa method and apparatus for driving a looped travelling band or formingA an upper run extending from a breast roll at'the rear end to a suction couch roll at the forward end of the top reach of the wire, with suction boxes beneath the top reach and adjacent the couch roll, and the bottom reach-` or return reach of the looped wire is: supported on` a number of return rolls. Heretofore, it had been the accepted practice to drive the forming wire through the suction couch roll (or suction couch rolls, if a pair of suction couch rolls are used at the forward endffof the loop). Helper drives might connect the main drive (as`- sociated with the suction couch roll)`to drives for other rolls, so that these rolls might be driven at: the speed of the traveling wire to avoid frictional` drag duringengagement therewith, but were not used to` drive the wire. In

the case of the breast roll, drive mechanismsvtherefor had not been successful, because of the tendency lfordriving the breast roll to cause irregularities in the smooth operation of the wire just beyond the breast roll whereat initial web formation takes place. The minimum tension on the wire occurs generally in the region of the breast roll (assuming the breast roll bearings to `be frictionless). As the wire passes over the suction boxes, a substantial frictional drag is applied to the Wire and the tension on,

the wire is at a maximum between the suction boxesfand the (first) suction couch roll. Depending upon the general type of the paper machine, this mmimum tension in present day paper machines may range from as little as about 20 pounds per inch to as'much as about 100 pounds per inch, but is usually about 30-60 pounds per inch (of width).

As a typical example of a modern-day paper machine operation, the wire may be about 200 inches wide and have a travelling speed of 2000` feet per minute with a total Fourdrinier load of 250 horsepower, The suction couch roll in such a paper machine is the drive roll. Since an appreciable amount of tension must be maintained on the wire at all parts of the travel` thereof, the tension on the wire at the oifr-unning side of the suction couch roll is usually about 12 pounds per inch. The maximum tension between the suction boxes and the suction couch roll (or at the forward side of thesuction boxes) is l2 pounds per inch plus theV amountof tension imparted to the wire by the 250 horsepower work input at the couch roll, which may be calculated as follows:

25o H.P. ss,ooo ft.1b./min.

2000 ft/minxaoo in. '206 lb'luf Total max. tension:l2t-l-20.6=32,6lb./in,

The foregoing indicates the operating conditions for a typical paper machine; and operating conditions such `as these have been used for `a number of years in paper Patent l machines. The operation herein described often results in a wire change about once every three to live days, which is necessitated by ordinary wear on the wire. The wire change involves a production shut down of an appreciable period of time plus the cost of a new wire (which itself may be as much as $4,000.00), although the production yloss is the greatest nancial loss 'here involved, For years, this has been recognized as one of the necessary costs of the operation of a paper machine, because it was universally assumed that the wire Wear wasl caused primarily by the suction boxes. It willalso be appreciated that, in viewof the extremely expensive nature of paper machines and also the highly developed skill of engineers installing such paper machines, the paper machine operators do not make random changes in the operation of the paper machines, `nor do-they look with any favor toward suggestions by their own or the installing engineers` concerning radical departures in the paper machine arrangement. losses, when the operation of the usual paper machine was at least sufficient to produce what amounts to anV economically adequate result.

The instant invention is based upon a discovery that much greater wire life can be obtained in any one of three ways. First, the main drive or driven roll from the suc tion couch roll may be changed to a plain-surfaced roll outside of the wire loop, which frictionally engages the outside surface rather than the inside surface of the wire loop. By the use of this first arrangement and by the use of such plain-surfaced roll (or rolls) to effect from 'at least about 50% to about 100% oi the tension drop in the wire, between the maximum tension and the minimum tension, it has been found that the wire life may be increased from the customary three days to as much as two or three Weeks. As those skilled in the art will readily` yappreciate this amounts to a spectacular saving in production time and materials.

It has further been discovered that substantially greater wire life may be obtained by driving the wire with a plain-surfaced roll within the wire loop and by providing a low normal force between the wire and the driving roll. This is in contrast to t-he high normal force heretofore employed at the suction area of the couch roll, and thought to be essential by those skilled in the art for driving the wire, for the reason that the suction effect would presumably give the best traction or the least slippage be# tween the suction roll and the wire.

In connection with the third manner of greatly decreasing wear and tear on the wire, U.S. Patent No. 2,392,150 (issued to Lloyd Hornbostel `and Edward D. Beachler, and assigned to the assignee of the instant application) describes a paper machine arrangement wherein a main suction couch roll land a primary suction couch roll are employed in the driving of the Fourdrinier wire. In this arrangement, the main suction couch roll is the driven roll and the primary suction couch roll is driven by a helper drive interconnectingthe main suction couch roll and the primary suction couch roll. This helper drive mechanism is actuated in response to the vacuum in the primary suction couch roll which it drives. As described in said patent, the helper drive mechanism puts only a slight amount of driving energy into the primary suction couch roll when there is no vacuum in the suction area thereof, but when avacuu-m builds up in the suction area thereof (because of more complete web formation on the wire) and` there is better traction between the wire and the suction roll, then the helper drive "imparts a substantial amount off driving energy to the primary suction couch roll.

In contrast, lthe invention is based upon a discovery that greatly decreased wear and tear on the wire can beV obtained by employing a` main driving roll` that has an Patented July 18, 1961` There is too much at stake to risk such substantialirnperforate rather than perforate surface (such as the surface of the main suction couch roll in said patent); and employing a helper drive between the main drive and perforate surfaced rolls (such as the primary suction couch roll of said patent) which imparts decreasingly smaller amounts of driving energy to the perforate surfaced roll in response to increases in vacuum at the roll suction area and/or in response to increases in vacuum at the suction boxes just ahead of the primary suction couch roll. In addition, the instant invention contemplates in the third embodiment the use of helper drive mechanisms connected between the main drive roll and other imporforate surfaced rolls, so as to drive such rolls in response to increases in vacuum in the suction couch roll and/or suction boxes, so that such rolls will take a proportionately greater amount of driving load with corresponding increases in the vacuum at the suction couch roll and/ or the suction boxes, The use of the three summarized forms of the invention results in greatly improved drives for paper machine forming wires as Well as a greatly decreased rate of wear and tear on the Wire, so that the usual wire life of the prior art of about three days may now be extended to as much as two,

weeks.

It is, therefore, an important object of the instant invention to provide an improved method and apparatus for driving a paper machine forming wire, or similar travelling band.

, It is another object of this invention to provide a method of handling a looped Fourdrinier type forming wire that comprises supporting and tensioning the wire on a suction couch roll, a breast roll and guide rolls, and frictionally engaging the wire with a plain-surfaced roll adjacent said suction couch roll and driving said wire thereby.

. It is still another object of the present invention to provide an improved Fourdrinier type paper making machine, comprising a looped forming wire, a perforate surfaced couch roll within the loop of said wire at one end thereof, a breast roll within the loop of said wire at the other end thereof, a plain-surfaced roll frictionally engaging the wire, and drive means rotating said plainsurfaced roll to drive the wire therewith.

It is a further object of the instant invention to prov ide an improved method and apparatus for driving a Fourdrinier type paper machine forming wire that comprises engaging the outside of the wire loop with the plain-surfaced roll and driving said roll to impart substantially all of the driving energy to the wire that is required to cause the Wire to travel in the manner desired.

Yet another object of the instant invention is to provide an improved method of handling a looped band or Wire that comprises engaging the inside of the band with a plurality of spaced perforate and imperforate surfaces, supporting and tensioning the looped band by urging said surfaces against the inside thereof, drawing a vacuum at the perforate surfaces to urge the band thereagainst, and engaging the outside of the band with the driven imperforate surface roll to move the band peripherally over the spaced surfaces inside the loop of the band.

Another object of the instant invention is to provide a method of handling a looped band that comprises supporting and tensioning the band on spaced perforate and imperforate surfaces and frictionally engaging the band with one of said imperforate surfaces while driving the same to drive said band. l Still another object of the instant invention is to provide an improved Fourdrinier type paper making machine, which compirses a looped forming wire, a plurality of rolls supporting said wire including a perforate surfaced suction couch roll within the loop of said wire and a plain-surfaced roll engaging the wire, and drive means rotating said plain-surfaced roll for driving the wire 'by means of said plain-surfaced roll.`

Another object of the instant invention is to provide an improved control method and apparatus for the driving of a Fourdrinier type forming wire in a paper machine using spaced perforate and imperforate surfaces to mount the wire, while driving the wire with a main drive connected to an imperforate roll surface and helper drives connected to the other surfaces and actuated in response to the vacuum in the suction couch roll and/ or suction boxes.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.

- On the drawings:

FIGURE 1 is a diagrammatic elevational View of a Fourdrinier machine wire arrangement of the prior art;

FIGURE 2 is a diagrammatic elevational view of a Fourdrinier machine wire arrangement incorporating the iirst embodiment of the instant invention;

, FIGURE 3 is a detail elevational view of the couch roll of FIGURE 2;

FIGURE 4 is a diagrammatic elevational view of a modification of the first embodiment of the invention;

FIGURE 5" is a diagrammatic elevational view of a Fourdrinier machine wire arrangement incorporating the second embodiment of the present invention;

FIGURE 6 is a view generally similar to FIGURE 3, and showing the couch roll of FIGURE 5 in elevation;

FIGURE 7 is a diagrammatic elevational view of a modification of the second embodiment of the invention;

FIGURE 8 is essentially a diagrammatic elevational View showing a Wire arrangement for a prior art machine upon which the third embodiment of this invention is an improvement;

FIGURE 9 is essentially a diagrammatic elevational view of a Fourdrinier machine Wire `arrangement incorporating the third embodiment of this invention; and

FIGURE l0 is an enlarged view of a portion of the drive mechanism shown in FIGURE 9.

As shown on the drawings:

In order to more fully understand the first and second embodiments of this invention, which will now be first described in that order, there is shown in FIGURE 1 the wire arrangement for a Fourdrinier type machine, indicated generally by the reference numeral 10 and comprising a looped forming wire 11 and a plurality of rolls supporting the wire 11, including a perforate surfaced suction couch roll 12 within the loop of the wire 11, a breast roll 13, and plain-surfaced return rolls 14 and 15. An adjustable tensioning roll 16 may also be employed to maintain tension on the wire 11 throughout its entire travel by adjustment in the direction indicated by the double headed arrow in the drawing.

The upper run 11a of the wire 11 passes over the breast roll 13, at which an inlet box 17 flows stock onto the upper run 11a of the wire 11. The direction of travel of the wire 11 is indicated by arrows; and it Will be seen that the rear end of the upper run 11a passes over the breast roll 13 and the wire 11 travels forwardly therefrom over the suction boxes 1-8 which are stationary and which deWater the web carried on the wire 11 as it passes over the suction boxes 18. The wire 11 then travels forward from the suction boxes 18 and over the couch roll 12 having a suction area 12a defined by a suitable suction gland 12b. The lower run 11b of the wire passes over the return rolls 14 and 15 and the tensioning roll 16, although there may be a number of additional plain or imperforate surfaced guide rolls employed in a similar manner.

In the prior art machines, suitable drive means in the form of a motor 19 was connected to the couch roll 12 through a driving connection such as a pulley and belt assembly 20 here indicated, and substantially the entire driving force for the wire was imparted thereto at the escasas couch 'roll 12'. Y For example, the tension Ti just afterthe. suction boxes 1584 would be 32.6` pounds per inch, and the` tension T2 just after the suction` couch roll would be 121 pounds per inch. The tension change over the return rolls 14 and 15 and the breast roll1`3 would be negligible so that the tension T3 justbefore the suction boxes 1'8` would also be about 12 pounds per inch. ln actual practice, the maximum tension T1 between the suction boxes 118 and the suction couch roll 12 may range from as little as about 2O pounds per inch to as much as about 100 pounds per inch, although the maximum tension` T1 is usually 30-60 in most paper machines. boxes 18 are stationary and theyu apply a rather substantial drag to the wire 11 passing over, so that the tension T3 before the suction boxes 13 is` within the range of about to about 50% of the maximum tension Tf1, but in no case in the prior art has T3. exceeded pounds per inch.

Expressed in other terms, the tension increase (T1-T3) across the suction boxes 18 is usually about l() to 60 pounds per inch; and in the prior art the couch roll 12V furnished 80 to 100% of the wire drive, thus creating a tension drop T1-T2 thercacross substantially equal to "Y1-T3. Using an arrangement such as` that here described, the wire 11 must be changed about once every three to ve days. employed for return rolls suchV as the rolls 14 and 15 near the couch roll 12 so that such return rolls will be driven at approximately the speed of the wire 1-1 to avoid frictional drag on the wire, but such helper drives do not reduce the rate of wear of the wire. As previously mentioned, a separate drive for the breast roll 13 is not ordinarily practical because it is important that the wire top run 11a be uniformly tensioned when it receives the stock from the head box 17.

Referring now to FIGURE 2, which shows an embodiment ofthe instant invention, indicated generally by the reference numeral 100, it will be noted that there is a looped forming wire 111j supported lby spaced perforate and irnperforate surfaces comprising a suction couch roll 112 having a suction area 11211 at the forward end of the top run 111a of the wire 111 and a breast roll` 113 at the rear end of the top run 111:1 whereas stock is received from an inlet box 117. The top run 111m is tensioned between the breast roll 113 at the rear and the,

couch roll 112 at the front end, andrsuction boxes 118 are positioned therebetween beneath the top run 1-11a. The lower run 11111 of the wire 111 is mounted on and tensioned by a plurality of rolls having imperforate surfaces, incluoing return rolls 114 and 115 mounted outside the wire loop and adjustable tension rolls 11'6a, 116b, 116C, and 11:15! mounted inside the loop of the wire and positioned so as to afford a substantial amount of wire wrap over the surfaces of the return rolls 11.4 and 115. A main drive mechanism, indicated at 119, is drivingly connected to the return roll 114 which, of course, frictionally engages the band or wire 11.1 on the outside thereof to drive the same. ln the usual paper machine arrangement, the main drive 119 is a speed regulated drive which has direct mechanical connection to the motor (as here indicated with double lines interconnecting the drive mechanism 119 and the roll 1.14 at 11921). The main drive 119 serves to control the actual wire speed.

Torque regulated helper drive mechanisms, such as the helper driver 120 for the return roll 115` are used preferably in the practice of the instant invention to impart rotary movement to certain other rolls, and particularly to the second return roll 115 for assisting the main drive roll 114 in driving the wire 111. ln the helper drive mechanism 120, the usual arrangement calls for a variable voltage D.C. electric motor which` drives the roll 115 at predetermined torque to impart predetermined drive to the wire 111. As will beappreciated,

The suction` ln some instances helper drives areable to impart an appreciable amount of the drive to the wire using at least one additional or helper drive roll 115.

It has also been found practical in the instant invention to employ a helper drive mechanism 121 to rotate the. suction couch roll 112. It is important, however, that the couchV roll 112 be employed to do a minimum amount of driving of the wire 111, if the advantages of the instant invention are to be obtained; in full. In this respect, the prior art concept of employing the couch roll as the main drive roll, for imparting 8G to 106% of the drive to the Wire, is contradicted by certain discoveries upon which the instant invention is based. Instead, the main driving effect` here obtained is obtained from the driven return rolls 114 and 115.

In the operation of the machine of `FIGURE 2, the tension T4 between the couch roll 112` and the suction boxes 118 may be about 55 pounds per inch and the minimum tension T5 just before the suction boxes 118 is about 20 pounds per inch. The helper drive mechanism 121 is regulated so that the couch roll is driven at the speed of the wire 111 but at a predetermined low torque to impart only a small amount of drive to the` wire, so that the tension in the wire 111 at 'T6 which is the oifrunning side of the couch roll 112, or the wire reach between the couch roll 112- and the first` return roll 1114 is about 50 pounds per inch. The remaining driven rolls 114 and 1'15, however, are driven so as to effect a tension reduction over each of about 20 to 50% of the overall tension` difference (T4 minus T5). In other words, the -lirst return roll 114 is driven so as to obtain an oifrunning tension T7 of about 35 pounds per inch; and the next driven return roll 115 is driven so as to` obtain an oirunning tension T8 of about 20 pounds per-inch, which is substantially the same as the tension T5 at the oncoming side of the suction boxes 118, since no driving (or at least no tension reduction) is contemplated at the breast roll 113. Operating the machine 10iin this manner makes it possible to increase the wire life to as much as two weeks or more instead of the previous wire life of from about three to about tive days. It should also be appreciated that driving the wire by return rolls (not shown) within the loop of the wire 111 rather than the couch roll 112 will also effect a very great reduction in 4the rate of wear in the wire; but the instant invention is based upon a discovery that a still greater reduction in the wire wear is obtained by driving the wire with return rolls, all or most of which are positioned outside the wire loop. In other words, whereas changing the drive from the couch roll to return rolls within the wire loop in a given paper machine increases y `the wire life from iive days to two weeks, changing the drive from return rolls inside the wire loop to return rolls outside the wire loop increases the wire life from two weeks to three weeks.

As will be appreciated, the helper drive mechanisms 119, and 121 here Shown are electrical devices, but it will be appreciated thatother types ofy helper mechanisms may be employed. For example, the main driven roll may be connected with another roll to be driven with a belt arrangement (not shown) cooperating with a helper drive device which actuates a pulley to tension or loosen the belt. In any event, the main drive mechanism regulates-the speed of the wireand ythe helper drive mechanisms are thus based in part for' their control on the main drive mechanism, since the helper drive mechanisms automatically assume the speed of the main drive mechanism and afford independent variation only in the torque imparted to the wire through the roll.

In general, it is desired tol reduce the tension drop across the couch roll 1,12 to a practicalminimum, because it has been discovered` that the tension drop across the couch roll 112 is a measure of creepage of the wire over the suction roll surface (because of the elastic character of the Wire) and such creepage has been found to be a key to the wearing of the wire. The exact functioning of this phenomenon will be explained hereinafter. On the other hand, it is generally not practical to merely drag the suction roll 1=12 with the Wire 111, so it has been found preferable to impart a suicient amount of drive to the suction roll 112 so that the Wire 111 is not required to drive it. In this Way, wear on the couch roll itself is minimized. It will be appreciated that the advantages of the invention may be obtained using a tension drop across the couch roll 112 of 0 (or even of a minus figure which would involve dragging the wire over the couch roll), but it is ordinarily not practical to attempt to drop the tension loss over the couch roll 112 to less than about 2 pounds per inch. Partial advantages of the instant invention may be obtained if the tension drop across the couch roll 112 is as high as perhaps l5 pounds per inch, but a tension drop of about 2-5 pounds per inch is most practical and advantageous.

` It will be noted that in the embodiment 100 of FIG- URE 2, the rolls 114 and 115 are plain-surfaced rolls. Additional rolls may be used, of course, and in such case it may not be necessary to employ quite as extensive a wrap of wire over the return roll surfaces as is shown in FIGURE 2. are not only plain-surfaced but as smooth as is reasonably practical, or covered with a smooth surfacing or even a yieldable surfacing material that is not too readily abraded (such as a relatively hard rubber surface) so that a minimum of wearing of the wire will take place when driven by such rolls. Of course, the frictional engagement between the smooth surfaced rolls 114 and 115 is in any case sufcient to actually drive the wire 111. A creepage which is unavoidable, however, is that resulting from the tension change caused by driving engagement with the roll surface. `In other words, it is impos sible to drive the wire without changing tension of the wire and since the wire is elastic (having a modulus of approximately 6G00 to 12,000 pounds per inch) it is impossible as a practical matter to avoid changing the length in this elastic medium with the change in tension. The change in length may be as much as to lO feet per minute on a machine running 2000 feet per minute, and it results in a very substantial Wearing effect upon the wire, if the Wire accomplishes this change in length while passing over a drilled or perforate surface of a roll such as the suction couch roll. Such slippage over smooth surfaced rolls such as the rolls 114 and 115 does not result in comparable wear on the Wire. The instant invention is based upon a further discovery that wire life may be greatly increased by employing driven smooth surfaced rolls outside of the wire loop. In this way, it has been found that the wearing effect of the driving rolls takes place substantially or completely (if all of the driven rolls are on the outside of the loop) on the side of the wire which does not contact the suction boxes L18. This is believed to explain the increased wire life resulting from the practice of the instant invention.

A serious misconception by the prior workers was that all of the wear on the wire was caused by the suction boxes. Another misconception by the prior Workers in the art, or assumption which has now been proved to be erroneous, is that the best driving eifect was supposed to come from a suction rroll such as the suction couch roll because of the better lfrictional engagement between the ywire and the surface of the suction couch yroll (brought about by the application of the vacuum). It is believed that the error in these assumptions can best be explained by the present findings which bring out clearly that so much creepage or slippage is required for so much change in tension using a `given elastic medium such as the Wire. Since this creepage cannot be avoided if the tension is going to be changed at a given roll, it now `follows (as a practical matter which can be It is preferred that these driving rolls 8 proved) that the greater the normal pressure of the wire against the roll, the greater the wear. This is contrary to all of the basic assumptions made by the prior workers in the art, and even though it can now be explained as a matter of hindsight in a rather logical manner, it was never appreciated heretofore.

It should further be noted, that the total failure of the prior workers in the art to appreciate that wear on the vWire vwas taking place at a driving roll as well as the suction boxes prevented the prior workers in the art from appreciating the advantage of driving the wire by frictional engagement against the outside of the wire loop, rather than the inside of the wire loop which engages the suction boxes.

From a process point of View, the invention involves a method of handling a looped band or wire, which comprises engaging tihe inside of the band with a plurality of spaced perforate (112 and 118) and imperforate (116a, 116b, etc.) surfaces, supporting and tensioning the looped band 111 by urging said surfaces against the inside thereof, drawing a vacuum at said perforate surfaces (112 and 118) to urge the band thereagainst, and engaging the outside of the band with one or more driven imperforate surfaces (L14 and `115) to move the band peripherally over the spaced sur-faces inside the loop of the band. The band 111 has `the tension therein decreased over the driven roll 114 30` to-l00% of the difference between the maximum and the minimum tensions T4 minus T5 in the travelling band 111. The normal pressure at the driven roll i1=14 or '115, wherein the tension is decreased 30 to 100% of the difference between the maximum and minimum tensions preferably does not exceed 3 pounds per square inch. 4

Referring now to FIGURE 3, which shows only partially the `wire 11.1, suction couch roll 112 and tensioning roll 116a of FIGURE 2, it Will be noted that it is preferable to maintain a tension drop (T4 minus T6) across the couch rol-l 1112 of 0 to about 25% of the overyali tension difference (T4 minus T5) in the operation of the machine. In contrast, in the prior art the tension drop T4 minus T 6 over the couch roll would be 80 to of the overall tension drop. Still another misconception in the art was that the slack running of the return reach of the wire was preferred. Accordingly, the tension on the return reach of the wire was maintained at a practical minimum and in no instance exceeded about 15 pounds per inch. The usual return tension recently employed in the prior art is about l2 pounds per inch. In contrast, it has been found that distinct advantages in the reduction of wire wear may be obtained by employing a distinctly higher return tension. In other words, by employing a return tension immediately after the suction couch roll (here indicated in the drawing atT) of about 20 to 40 pounds -per inch (and preferably 30 pounds per inch) a`distinct reduction in the wire wear results. wire of about 20 to 40 pounds per inch thus affords distinctly advantageous reduction in wire Wear. It will be appreciated that the maximum tension T4 at the olirunning side of the suction boxes in any ysuch paper machine will have to be greater than the increased minimum tension of 20 to 40 pounds per inch in order to operate the machine, but this is presumed since the tension of 20 to 40 pounds per inch' is specified as the minimum tension, as contrasted to the maximum tension herein described.

The advantages of the foregoing may be explained by reference to FIGURE 3,- wherein it will be noted that the suction box 112a within the suction couch roll 112 has an angular dimension s of perhaps 3040 but the wire 11 also wraps an additional x degrees of the roll periphery, x being ordinarily within the `range of 'about l30 to about 120 inthe usual paper machine operation.

There is a mathematical relationship between the oncoming tension T4, the otfrunning tension T4, the co- The minimum tension in the eiicient of friction y between the wire and the imperforate roll surface, and the angle of wrap x expressed in radians as z, which relates to the surface of the roll `112 over which creepage will take place.

The mathematical relationship may be expressed as follows:

t T4=T6eyz wherein e is the natural logarithm base and x and z are above indicated. According to the above form-ula, the actual driving effect or tension reduction in the wire is obtained only in that portion ofthe wire wrapped around z radians of the roll surface. In ordinary practice the Wire or any other driven band will be Wrapped around more than z radians, or the rroll will tend to slip noticeably. In the practice of the instant invention, however, it has been found to he particularly important to avoid any driving effect against the wire at the suction box 112e of suction couch roll `112. Accordingly, driving in the suction couch roll must take place only over the angle x or over a smaller angle. One Way to accomplish this is to increase the angle of wrap x beyond the suction box, but this has some certain limitations. Another Way to accomplish this purpose, ywhich has never been appreciated heretofore, is increasing the tension T6 on the otfrunning side. This results in a smaller tension drop T4 minus T6. It will thus be appreciated that one aspect of the instant invention resides in the process concept of driving the couch roll so as to obtain a Wire tension T6 after the couch roll that is more than el/Z In this way, drive is obtained only on the surface of the couch roll which does not have vacuum applied thereto; f#

and it will now be explained why still another prior art concept is erroneous, namely the prior art concept that the higher normal Ipressure at the suction area aiorded better traction and hence more advantageous driving for the wire.

It will be appreciated that a material reduction in wire wear is obtained by increasing the tension on the return side of the wire coupled with driving the wire with plainsurfaced rolls outside of the wire loop, in accordance with the conditions just described.

Referring now to FIGURE 4, there is shown only partially a wire arrangement 200, comprising a Wire 2111 passing over suction boxes 218, a suction couch roll 212 having a suction area 212a, a turning roll 221, a return roll 214 outside of the wire loop, a return roll 222 inside the wire loop, a return roll 215 outside the wire loop and nally a tensioning roll 216. In this embodiment, the main dn've means 219 drive the first return roll 21'4 that is positioned outside of the loop and a helper drive 220 driv the next return roll 215 that is positioned outside of the loop. The rolls 214, 215, 221 and 222 are all plainsurfaced rolls. Helper drive mechanisms are `also provided for cert-ain rolls within the Wire loop, such as a helper drive mechanism 223' for the suction couch roll 212, a helper drive mechanism 224 for the turning roll 221 and a helper drive mechanism 225 for the return roll 222 positioned within the loop. It will be appreciated, however, that in order :to `obtain the advantages of the instant invention a substantial portion (if not all) of the driving of the wire must take place over the return rolls 214 and/'or 215 positioned outside ofthe wire loop. In other words, at least about 50%, and preferably about 75% of the overall tension difference in the Wire must be made up by the driving effect of the rolls 214 land/or 215, in order to obtain the advantages of the invention.

In the machine 200, the tension T9 before the suction boxes 213 is 20 pounds per inch and the tension T10 between the suction boxes 218 and the suction couch roll 212 is 55 pounds per inch. The overall tension diierence is thus T10 minus T9 or 35 pounds per inch. The helper drive 223 imparts a minimum amount of drive to thesc'- tion couch roll 212 so that the tension T11 at the offrunning side of the couch roll 212 is about 50 pounds per inch. The helper drive 224 also imparts a minimum of drive to the turning roll 22'1, or at least a relatively small amount of drive, so that the tension T12 at the oifrunning side of the turning roll 221 is 45 pounds per inch. The main drive 219 imparts an appreciable amount of torque to the return roll 214 so that the tension T13 at the offrunning side thereof is reduced to about 35 pounds per inch; the tension at the otrunning side of the return roll 222 is about 30 pounds per inch (because this roll is also inside the loop) and the tension T15 at the orunning side of the second return roll 215 outside of the. loop is approximately 20 pounds per inch.

The arrangement of FIGURE 4 involves driving the wire to a substantial extent with plain-surfaced rolls positioned outside the wire loop, but a certain amount of driving effect is also obtained from the rolls positioned within the wire loop. As will be appreciated, there are certain other practical considerations involving the mounting of the rolls, the positioning thereof, the abruptness of changes in direction in the wire travel, etc. which are involved in the operation of paper machines and which may be used to afford certain advantages. For this reason, the arrangement of FIGURE 4 may be in some instances more advantageous practically than the arrangement of FIGURE 2 wherein substantially the entire driving elect was obtained from the rolls 114 and 115 outside of the loop. Nevertheless, in each case a substantial amount of the driving effect is obtained from rolls outside of the wire loop, or at least about 50% of the driving effect is obtained from such rolls.

With respect to driving on plain-surfaced rolls it must be appreciated that the rictional engagement between the Wire and such rolls may be less than in the case of perforate surfaced rolls. Accordingly, it has also been found important to have a certain minimum amount of total Wrapped area, or expressed in other terms, a total number of degrees of wrap for the plain-surfaced driving roll or rolls. As mentioned, it has been found preferable to use a minimum of about 2 plain-surfaced driving rolls. Three plain-surfaced driving rolls give excellent results, and at least two of these rolls should be positioned outside of the loop, as shown in FIGURE 4. It will be appreciated also that the plain-surfaced rolls are of appreciable diameter (so as to avoid unnecessarily high normal forces) in order to stand up under the relative forces applied thereto in ordinary paper machine operation. The rolls are ordinarily from about one-half to about equal the diameter of the couch roll in size. Each of the plain-surfaced driving rolls employed in the practice of the instant invention should be positioned with respect to the other rolls and the various tensioning rolls so as to have a wrap of at least about 40. In otherv words, at least about 40 of the peripheral surface of the roll should be wrapped by the wire, if such roll is to be employed for driving purposes. As will be noted from FIGURE 2, the wrap for each of the rolls 114 and 115 is at least about 180. In FIGURE 4, the Wrap for each of the return rolls 214, 2'15 and 222 is at least about 90"; and the wrap for the turning roll 221 is at least about 180. This is a total wrapped area of about 360 in FIGURE 2 and about 450 in FIGURE 4.

In the practice of the rst mode of the instant invention the total wrapped area should be at least about 180, for rolls inside and outside of the loop; and the total wrapped area for rolls outside of the loop should be at least but preferably is a minimum of about 180.

Another feature of the first embodiment involves the control of the normal pressure exerted by the wire against driving rolls. As previously mentioned, a minimum normal pressure has been found to be desirable, rather than the maximum normal pressure which the prior workers in the art considered necessary. Without going into 1 1 elaborate calculations, it will be noted that the pressure in pounds per square inch resulting from the wire tension along onV a given roll is approximately the average tension divided by the radius in inches of the roll. In FIG- URE 4, the average tension is 521/2 pounds per inch across the couch roll 212, which is 22 inches in diameter, from which the pressure in pounds per square inch may be calculated as approximately 2.4. The normal pressure across each of the other rolls will be reduced somewhat because the average tension is reduced but may be increased slightly because the radius of the return rolls may be slightly smaller. The normal pressures will in each case be approximately 2 pounds per square inch,-

however.

Using a `vacuum of 20 inches of Hg in the suction area 212a, and assuming the effective land or support area to be only about 45% of the total area, it will be found that the pressure in pounds per square inch applied by the vacuum is about 22,

If a lump breaker roll, such as the rol-l 250 is also associated lwith theY couch roll 2112 in nip defining relationship, it will be appreciated that a still greater normal pressure in pounds per square inch will be applied. This pressure will depend upon the nip pressure as well -as the Anip area-and other Yfactors which need not be computed, since it is apparent that the normal pressure will bei increased by the presence of a roll such as the roll 250.

`In contrast, the normal pressure against the main driven roll 214 is that created by the tension in the wire or approximately only 2 pounds per square inch. At leastl about 1/2 pound per square inch should be used. It will be noted, however, that it is particularly important t employ normal pressures not more than about 6 to 8 pounds per square inch, and preferably not more than about 3 pounds per square inch against driving rolls, or rolls which effect appreciable tension changes. The amount of normal prwsure employed should be just that amount sufficient to obtain the desired frictional eiect for driving, but insufiicient to accelerate the wearing effect on the wire caused by creepage.

-As earlier indicated, substantial lessening of wear and tear on the lforming wire is accomplished by driving the wire with a plain-surfaced roll, and by providing a low normal force between the wire and the driving roll, in contrast to the high normal force heretofore employed at the suction area of the couch coll. As was also stated, it has been the practice to drive the `forming wire with a suction roll7 whereat the suction effect would presumably give the best traction or the least slippage between the roll and the wire. However, as will now be described in connection with FIGURES 5, 6 and 7, portraying the second embodiment of this invention, great improvements in the reduction of wire wear are accomplished by supporting and tensioning a looped band on spaced perforate and imperforate surfaces, and frictionally engaging the baud with one of said imperforate surfaces while driving the same to drive said band.

The preceding discussion making reference to the prior art drive arrangement of FIGURE l applies equally to the second embodiment of the invention or to the second manner of driving the forming wire to reduce wear thereof. However, it may be seen upon reference to FIGURE 5, showing one form of the second embodiment, that the generally designated apparatus 300 comprises a looped forming wire 311 supported by spaced perforate and imperforate surfaces in the vform of a suction couch roll 312 having a suction area 312a at the forward end of the top wire run 3110, and a breast roll 313 at the rear end of said top run, whereat stock is received from an inlet box 3117. In the manner of the arrangement of FIGURE 2, the top run 311@ in FIGURE is tensioned between the Abreastwroll 313 at the rear and the couch roll 312 at the front end, while Vbeneath said` top run `there tioned suction boxes 318. l

The lower run 311b lof the wire 311, on the other hand,

is mounted on and tensioned by a plurality of rolls having imperforate surfaces', including return rolls 314, 315 and 315a, and it may be seen that between said rolls there is provided adjustable tensioning rolls 316:1, 316b and 316C. A main drive mechanism 319 is drivingly connected to the return roll 314 which frictionally engagesl the band or wire 311 to drive the same. The main drive 319 serves to control the actual wire speed, and said, drive may be the same as the drive 119 in FIGURE 2' and interconnected with the roll 314 at 319m. 1

Torque regulated helper drive mechanisms 320 and 320d impart rotary movement to the return rolls 315 and. 3l15a for assisting the main drive roll 314 in driving the;

wire 311, as earlier `described in connection with FIG-1 URE 2. The helper drive mechanisms 320 and 320,11;- may be variable voltage D.C. electric motors driving` the connecting rolls 315 or 3115i: at predetermined torque to impart predetermined drive to the wire, or on the other.

hand, the helper drive arrangement may be used merely to rotate the roll 315 at the speed of the wire to prevent dragging the wire thereover. However, as noted earlier, it is definitely preferable'to impart -an appreciable amount of drive to the wire, using at least one additional or helper drive roll 315, and preferably two rollls 315 andL Also in the manner of FIGURE 2, the arrangement ofi FIGURE 5 incorporates a helper drive mechanism 321 which rotates the suction couch roll 312 so that said roll only does a minimum amount of wire driving. The main driving effect is obtained from the driven return rolls, and as was described, the discoveries upon which the instant invention is based contradict the earlier concept of employing the couch roll as the main drive roll for imparting to 100% of the drive to the wire.

The wire tension values at various locations on thev machine of FIGURE 2 have been noted hereinabove, and simplicity of description it may be stated that the tension T12 in FIGURE 5 corresponds to T16 in FIG- URE 2. Similarly, the minimum tension T13 before the suction boxes 318 is equivalent to T11 in FIGURE 2, and

the helper drive mechanism 321 to the couch roll 312 isV inch. Return rolls 3115 and 315a, on the other hand, are

driven so as to obtain offrunning tensions T21, and T21, respectively, of about 30 and 20 pounds per inch, It may be noted that offrunning tension T21 is substantially the same as the tension T13 at the oncoming side of the suction boxes 318. By thus frictionally engaging the wire after the suction couch roll with a plain-surfaced roll and driving the wire therewith to maintain a tension drop4 across the couch roll of zero to 25% of the difference in' tension across the suction boxes 318, it is now possible to increase the wire life to as much as two weeks or more, instead of the previous wire life of from about to three to about iive days. In this connection, specific values of tension drops across the couch roll 112 of FIG- URE 2 were earlier noted, and these same values applyV to the suction couch roll 312 of FIGURE 5. In addition, the earlier discussion specifically directed to FIGURE 3 is applicable to FIGURE 6, including reference to the mathematical relationship between the oncoming tension T4, the offrunning tension T6, the coeiiicient of lfriction y between the wire and the imperforate roll surface, and' t-he angle of wrap x expressed in radians as fz`. YOf

acentos 13 course, inthe earlier stated equation when applied to the machine 300 of FIGURES `and 6, T4 is equivalent to T12 and T6 is equivalent to T14- From a process point of view, the invention as defined in the second embodiment of FIGURES 5, 6 and 7 involves a method of handling a looped band or wire, cornprising engaging the inside of the loop of the band or wire 311 with a plurality of spaced perforate (312 and 318) and imperforate (314 and 315) surfaces, supporting and tensioning the looped band 3111 by urging said surfaces against the inside thereof, drawing a vacuum at said imperforate surfaces (312 and 318) to urge the band 311 thereagainst, and engaging the band 311 with the driven imperforate surfaced roll (314) to move the band 311'1 peripherally over the spaced surfaces inside the loop thereof; As in the machine 100 of FIGURES 2 and 3, the band 3-11 in FIGURES 5 and 6 is decreased in tension over the driven roll 314 30 to 100% of the difference between the maximum and minimum tensions in the traveling band 311, and said difference preferably does not exceed three pounds per square inch.

` Referring now to FIGURE 7, disclosing a modified form `of the second embodiment of this invention, there is shown only partially a wire arrangement 400. It may be observed that FIGURES 4 and 7 have a number of common elements, identified in the latter view by the numerals 411, 412, 412a, 418, 421, 424 and 450. A further description of these elements is accordingly not believed necessary.

In the arrangement of FIGURE 7 a return roll 440 is provided over which the wire 41'1 is wrapped, and the return roll 440 may or may not be positively driven. The turning roll 421 is driven by main ydrive means 422, whereas in FIGURE 4 the turning roll 221 is driven by a helper drive mechanism 224. In FIGURE 7 a return roll 414 is driven `by a helper drive 419, and the wire 411 passes overa tensioning roll 416. As in FIGURE 4, the turning roll 421 of FIGURE 7 is a plain-surfaced roll and nota suction roll.

In the machine 400 of FIGURE 7, the tension T9 before the suction boxes 418 is pounds per inch, the tension T23 between the suction boxes and the suction couch roll 412 is 40 pounds per inch, and the turning roll 421 is the driving roll which drives the wire- 411 so as to produce a tension T24 of 35 pounds per inch between the suction couch roll 412 and the turning roll 421. Without going through elaborate calculations, it will be noted that the pressure in pounds per square inch at the suction area 412a of the suction couch roll is 4approximately the average tension divided by the couch roll radius in inches. In this instance, the average tension s 371/2 `pounds per inch and the couch roll radius is 22 inches, which means that the pressure in pounds per square inch is about 1.6.

Using a vacuum of 20 inches of mercury in the suction area 412a, and assuming the effective land or support area to be only vabout 45% of the total area, it will be found that the pressure in pounds per square inch 4applied by the vacuum is about 22. Ifa lump breaker roll such as the roll 450 is also associated with the couch roll 412 in nip-dening relationship, it will of course be understood that a still greater normal pressure in pounds per square inch will `be applied, This pressure depends upon the nip pressure, nip arealand other factors which need not be computed, since it is apparent that the presence of the lump breaker roll will increase the normal pressure.

In contrast, the normal pressure against the turning roll 412 is that pressure created by the tension in the wire or approximately 1.6 pounds per square inch. At `least about `one-half pound per square inch should be used. It may be noted that it is particularly important tthat normal pressures not more than about six to eight pounds per square inch be employed, and preferably .this pressure is not more than about three pounds per 14 square inch against the driving rolls, or the rolls which eiect appreciable tension changes.

It was earlier noted that when driving on plain-surfaced rolls the frictional engagement between the wire and said rolls may be less than in the case of perforate surfaced rolls. -For this reason, it is important to have a certain minimum amount of total wrapped area, or as may be otherwise stated, a total number of degrees of wrap for the plain-surfaced roll or rolls. A minimum of about two plain-surfaced rolls is preferable, while three plain-surfaced rolls give excellent results. As was also noted, the plain-surfaced rolls are of appreciable diameter so as to avoid unnecessarily high normal forces, in order to stand up under the relatively high forces applied thereto in normal paper machine operation. Plain surface rolls employed in the practice of the method described in connection with FIGURES 2 to 7 are positioned` with respect to themselves and the various tensioning rolls so `as to have a wrap of at least about 40 as to the arrangement of l'FIGURE 5, the wrap for each of the rolls 314, 315 and 315:1 is at least about 90. In =FIG- URE 7, the Wrap for the turning roll 421 is about 180, and the wrap for a secondary helper driven roll 414 is about producing a total wrapped area of 300. As was also stated in connection with FIGURES 2 to 4, and this applies to FIGURES 5 to 7, the total wrapped area should be at least about The third method conceived by applicants to greatly decrease the rate of wear and tear on the forming wire uses spaced perforate and imperforate surfaces to mount the wire, while the wire is driven with a main drive connected to an imperforateroll surface and helper drives connected to the other surfaces and actuated in response to the vacuum in the suction couch roll and/or suction boxes. Referring now to FIGURE 8, the reference numeral 510 indicates generally a wire arrangement for a paper machine, comprising a looped forming wire yS11 having the upper run 511g thereof stretched between a suction couch roll 512 at the forward end and a breast roll 513 at the rear end, whereat a head box 514 Hows stock onto the upper run 51151 of the wire 511. Between the breast roll and the suction couch roll are mounted suction boxes 515 which are stationary and which serve to dewater the web passing thcreover on the wire 511. Dewatering is also accomplished at the suction area 512a of the suction couch roll 512 and at a suction area 51651 of a main suction couch roll 515 in advance of the primary suction couch roll 512. As indicated diagrammatically, a motor 517 suitably connected to the main suction couch roll 516 through a belt and pulley arrangement S17 drives the suction couch roll 516; and this is the main drive for the wire 511.

Guide rolls 519, S20 and S21 are mounted to engage the lower or bottom run 51111 of the Wire 511 and a tensioning roll 522 (movable in the directions indicated by the double heated arrow) also engages the bottom run 51111 for the purpose of applying tension to the wire 511 to the extent desired.

In starting the machine 51), the suction on the suction boxes 5115 is turned off and also at the suction areas 51241 and 516:1, respectively. The main drive 517, 518 rotates the main couch roll 516 and this in turn starts the movement of the wire 511 which is frictionally engaged by the couch roll 516. A lhelper drive mechanisrn 523 interconnects the main suction couch roll 516 and the primary suction couch roll 512, and this mechanism (which will be described in detail hereinafter) comprises a belt 523m interconnecting drive pulleys on the rolls 516 and 512, a tensioning pulley 5'23b movable in the directions indicated by the two headed arrow, and a control box 523C (indicated in dotted lines) which is actuated by the vacuum in the suction yarea 512a and which serves to tension the ybelt 523a with increased vacuum in the vacuum area 512e, so as to impart greater driving force or energy to the primary couch roll 512 within increases in the vacuum in the suction area of the couch roll. The reason for this is -to obtain flrst better traction between the wire 511 and the primary suction couch roll 512, at the suction area 51241, before empolying the suction couch roll 512 to carry out appreciable driving of the wire 511. At the startup (before there is any yappreciable vacuum in the suction area 5112a), it is desired only to rotate the couch roll 512 at approximately the speed of the wire 511 so as to avoid having the wire 511 drag over the couch roll 512, and also to avoid having the couch roll 512 moving appreciably faster than the wire 511 and causing wearing of the wire because of lack of traction between the wire 5211 and the couch roll 512.

In the foregoing prior art device, which is shown in said Patent No. 2,392,150, the driving of the wire is accomplished by perforate surfaced rolls, whether or not the main driving eiect is accomplished by the suction couch roll 516 or by the combination of suction couch rolls S12 and 516. Although the arrangement 516 has certain advantages in the paper machine art, the wire life is still quite short using this arrangement. In general, the Wire life is about three to four days using the arrangement 510.

Referring now to FIGURE 9, wherein an arrangement embodying the instant invention is shown, it will be noted that the arrangement herein shown in FIGURE 9 affords the advantage of superior operating control of the paper machine and also `an increased wire life of as much as two weeks. In FIGURE 9, the embodiment 600 comprises a forming wire 611 defining a loop, a perforate suction couch roll 612 within the loop of the wire, having a suction area 612a, a breast roll 613 also within the loop of the wire 611 and cooperating with the suction couch roll 612 to define an upper run 611a of the wire 611 stretched therebetween. At the rear end of the upper run 611, over the breast roll 613, a flow box 614 ows stock onto the wire 611 and the wire carries the stock and the web resulting therefrom forwardly over suction boxes 615 and then over the suction couch roll 612 after the suction boxes 615.

In the arrangement of FIGURE 9, a wire turning roll 616 is preferably employed after the suction couch roll 1:12 (so that the web may be removed in the wire run between the suction couch roll 612 and the turning roll 616), and the turning roll 616 is an imperforate surfaced roll which reverses the travel 'of the looped wire 611, starting the bottom run of the wire 611 back to the breast roll 613. The bottom .run 611b of the wire 611 is also friotionally engaged by guide rolls 619, 620, and 621 plus a tensioning roll 622 which is movable in the directions indicated by the two headed arrow for the purpose of applying the desired tension to the forming wire 611.

In the embodiment 600, a main drive motor 617 is provided with a suitable drive connection 618 such as the pulley and belt arrangement here shown interconnecting the main drive 617 with a main drive roll, which is the plain-surfaced or imperforate surfaced guide roll 619. The main drive roll 619 imparts a substantial amount of the driving energy to the wire 611, but various helper drive means are also connected to the main drive roll 619 (and the .drive means 617, 618 associated therewith). For example, a first helper drive means 623 (which will be described in detail in connection with FIGURE 10) interconnects the main drive roll 619 and the suction couch roll 612. Secondary helper drive means 624 serve to interconnect the main drive roll 619 and the turning roll 616; another secondary drive means 625 serves to interconnect the main drive roll '619` and another guide and drive roll 620. Still another helper drive means 626 connects the guide roll 621 with the main drive 617, 618, but in this case the helper drive mechanism 626 makes such connection through the guide roll 116 620, instead of directlythrough the main drive roll 619.` Either type of helper drive arrangement may be used, however.

The helper drivemechanisms 623, 624, 625 and 626 are preferably actuated or controlled by pressure sensitive means which will be described which are connected with the suction area 612a of the suction couch roll and/or the suction boxes 615. Two types of pressure responsive arrangements are used. In connection with helper drive mechanisms 624, 625 and 626 which serve to drive plain-surface or imperforate surfaced rolls, it is desirable in the practice of the instant invention to impart greater driving force to these rolls as the vacuum increases in the couch roll suction area 612a and/or the suction boxes 61S, for the reason that such increases in vacuum indicates that a greater driving load is required in order to move the wire 611 at the speed desired, and such greater driving load is taken up by these plain-surfaced rolls 616, 620 `and 621 rather than the perforate surfaced suction roll 612. This is contrary to the teachings of the prior art, in that the prior art workers were interested in obtaining maximum traction or normal forces between the wire and the suction couch roll 612 before using the suction couch roll 612 extensively for driving purposes. In contrast, the instant invention4 contemplates using the suction couch roll 61'2 for a minimum amount of driving energy with increased vacuum in the suction area 612a or the suction areas created at the suction boxes 615.

As will be appreciated, the suction boxes 615 are stationary and they also present what amounts to a perforate surface over which .the wire 611 is dragged thereby resulting in wear on the wire 511 which cannot be avoided in a machine of this type. The suction couch roll 612 also presents a perforate surface, but this surface rotates so as to move peripherally with the wire 511 at the same peripheral speed. The peripheral speed of the wire 511 is the speed with which we are here concerned then this is the longitudinal speed of the wire as contrasted to a lateral or axial speed. As the vacuum increases in the suction boxes 615, with the same or an increasing amount of paper web on the wire, the drag at the suction boxes 615 increases and greater tension is required in the wire 611 at the offrunning side of the suction boxes 615, or between the suction boxes 615 and the couch roll 612. In like manner, an increase in the vacuum in the couch roll suction area 612a, indicates that the web is building up to a greater extent on the wire 611 and this increased web on the wire 611 will, of course, increase the drag on the wire 611 at the suction boxes 615. 'For this reason, the vacuum at either the suction area 612a or the suction boxes 615 will indicate generally the amount of 4driving force which must be put into the Wire 611 to maintain the speed desired. As `this amount of driving force required increases, it has been found important to put an increasing amount of driving force into plainsurfaced rolls such as the rolls 619, 620, 621 and 616, rather than the perforate surfaced suction couch roll 612, despite the fact that better traction is apparently obtained between the Wire 611 and the suction couchroll 612 under increased load conditions.

It is believed that the advantages of the instant invention can best be appreciated by a study of the tension changes in the forming wire 511 of the prior art and the forming wire 611 of the instant invention. In the prior art, using the tension igures hereinbefore discussed, the tension T25 just before the suction boxes 515 is the minimum tension applied to the wire and this may be about 512 pounds per inch (of width of the wire) which is e minimum amount of tension for the entire wire in such a paper machine. Because of the drag on the wire 511 caused by the suction boxes 515, the tension T26 after the suction boxes 515 and before the couch roll 512 is ata maximum of perhaps 33 pounds per inch in order to maintain the desired speed over the suction boxes 515.

If the primary suction couch roll 512 were employed to impart all of the driving energy required to the wire 511, then the tension drop across the primary suction couch roll 512 would be T25 minus T26 or `a tension drop of about 21 pounds per inch thus obtaining -a tension of T27 at the oimnning side of the couch roll 512 of 12 pounds per inch, the same as the tension T25. If the main couch roll 516 is used as the sole driving roll, the tension drop thereacross would be the same and the tension T23 at the orunning side of the main couch roll 516 would be l2 pounds per inch. If the two suction couch rolls 512 and 516 are both driven, and these are the only driven rolls here employed, then the tension T23 at the offrunning side of the main couch roll 516 will be 512 pounds per inch and the tension T27 between the rolls 512 and 516 will be something between 33 pounds per inch and 12 pounds per inch depending upon the -amount of load which each of the perforate couch rolls take up.

Although it would appear that the advantageous way to operate such a paper machine involves having a maximum traction or normal force between the wire 511 and the primary couch roll 512 before using the couch roll S12 for driving purposes, the instant invention is based on a discovery that there is more than this to the problem. It is true that, if the suction couch rolls S12 and 516 are to be used as the driving rolls, there are certain advantages particularly in the startup in employing the teachings of said Patent No. 2,392,150. It is also true that prior workers in the art have considered the suction couch roll (or rolls) as the only logical point at which driving force should be imparted to the Wire. The instant invention, however, is based upon the discovery that it is particularly advantageous to do just the opposite, namely, to use smooth surfaced rolls to drive the wire and to put a minimum amount of driving force into the wire using perforate surfaced rolls such as `suction couch rolls.

Although it is not desired to limit the invention to any particular theory, it is now believed that the explanation by hindsight for the improved wire life obtained in the practice of the instant invention resides in the fact that the instant Fourdrinier wires are all made with a substantial amount of elasticity, having an elastic modulus of from yabout 6 to about 10 pounds per inch. In fact, commercial wires now almost always have a modulus of `approximately 8600 pounds `per inch. Such elasticity means lthat the actual length of the wire may be changed appreciably by changes in tension applied to the wire. If the entire wire loop is under tension of 120 pounds per inch rather than the minimum tension of 12 pounds per inch here mentioned, the wire loop will be larger. Also, if a small section of the wire loop is under a much higher tension than another portion of the Wire loop, this small section of the wire loop will be stretched to a greater extent andthe same mass or quantity of wire will have a greater length in this high tension region. When a drive roll drives the wire, the drive roll effects arreduction in the tension in the wire. As mentioned, using either one of the rolls 12 or 16, or both, as the sole driving force in the machine 510 results in a decrease in the tension in the wire from 33 to 12 pounds per inch. The reduction in tension takes place while the wire is in contact with the roll surface; and calculations will establish that a reduction in tension of some 21 pounds per inch in the portion of wire engaging one of the suction couch rolls 512 or 516 (having a modulus of 8600 pounds per inch) results in a change in dimension of appreciable magnitude in the wire. Although this change in dimension is of appreciable magnitude so as to cause slippage between the wire and the roll surface, it is hardly observable with the naked eye, and the original thought among the workers in the art was that increased normal forces between the roll in the wire would cause besttraction and minimum slippage. The difhculty, however, is

18 that the tension change necessarily results in a dimensional change and consequent slippage. For this reason, increased norm-a1 pressures serve merely to magnify the wear on the wire, because the slippage due to the tension change in the wire cannot be eliminated.

The embodiment 600 of FIGURE 9, using the same general operating conditions as those described in conneotion with the embodiment 10i, the tension T20 at the oncoming side of the suction boxm 615 will again be 12 pounds per inch and the tension T30 at the oifrunning side of the suction boxes 615 will again be about 33 pounds per inch for a total tension drop of 2l pounds per inch. The suction couch roll 612, is however, driven only at approximately the average speed of the -wire 611 (so as not to drag on vthe `wire 611) thereby obtaining a minimum tension decrease over the suction couch. roll 612 resulting in a tension T31 at the offrunning side of the suction couch roll 612 of about 30 pounds per inch. `Any one of the remaining smooth surfaced or imperforatesurfaced rolls 616, 619, 620 or 621 may then be used alone to drop the tension T31 from 30 pounds per inch to the minimum tension of 12 pound per inch (T23), but it is preferable to drop the tension step-wise over two or more plain-surfaced rolls. For example, the tension T32 at the olif'running side of the turning roll 616 may be 25 pounds per inch, `so as to effect ya tension drop of 5 pounds per inch across this driven roll 616. It should also be mentioned that, if the roll 616 is a second suction couch roll, as the roll 516 in the embodiment 510, then the tension drop across the roll 616 should also be held to a minimum of perhaps 2 to 3 pounds per inch. The tension T33 across the main drive roll 619 should be reduced to 20 pounds per inch so as Ito etiect another tension drop of 5 pounds per inch. In like manner, the tension T34 between Iche rolls 620 and 621 can be dropped to 15 pounds per inch, and the last driven roll 621 may drop the tension to T29 or 12 pounds per inch. In an arrangement such as the arrangement 660, using the operating conditions just described, the wire life is extended from the normal period of 3 to 4 days to approximately two weeks. Substantially the same results are obtained using, for example, tensions of T23 equal to 2O pounds per inch, T30 equal to 55 pounds per inch, T31 equal to 50 pounds per inch, T32 'equal to 40 pounds per inch, and T33 and T10 equal to 20 p'oundsper inch (wherein it will be seen that no driving is 'accomplished wit-h the last two rolls 62@` and 621. It is also advantageous to employ a plain-surfaced roll 6210 positioned outside the loop of the wire 611 to do the bulk of the driving, because this roll 62@ engages the surface of the wire 6111 which does not come into Contact with such perforate surfaces as the couch roll `surface 612 and the tops of the suction boxes 615. In such instance, the tension arrangement may advantageously be T20 equal 20 pounds per inch, T30 equals 50 pounds per inch, T31 equals 53 pounds per inch, T32 equals 50 pounds per inch, T33 equals 45 pounds per inch, and T33 equals 25 pounds per inch.

An important aspect of the instant invention resides in the actuation of the helper drive mechanisms. As will be appreciated, the helper drive mechanisms can be set so as to respond to a given vacuum in a given manner. In other words, the main drive 617, 618 associated with the main drive roll 619 can be geared so that, in View of a predetermined approximate or average tension, a given amount of drive energy will be imparted to the wire 611 and this amount is sufcient at least to start up the wire 611 when there is no load on the suction yboxes (or at the couch roll suction area 612a). As the wire 6.11 is started up and a load (or vacuum) appears at the suction boxes `615 and the couch roll suction area 612a, greater driving force is necessary to maintain the wire speed. This driving force is imparted to certain rolls by the helper drive rnechanims.

Referring to FIGURE 10, it will be noted that the main drive roll 619 is connected to the turning roll 616 -by a helper drive mechanism indicated generally by the reference numeral 624 which comprises a slip belt 624:1 interconnecting drive pulleys 616e and 619a on the rolls, respectively. A tensioning pulley 624b engages the belt 624a and is movable on a shaft 624e to tension or relax the belt l62451. The shaft 624e carries pistons 624d and 624e coaxially mounted thereon land the shaft is held in position by a packing gland 624]L in a cylinder 624g receiving the pistons 624d and 624e. A spring 624k urges the tensioning pulley 6241) on the shaft 624C against the belt 624a to the extent necessary to accomplish minimum helper drive between the rolls 616 and 619. A chamber between the packing gland 6241 and the piston 624e is provided with an inlet 6241i through which a fluid line 630 passes so as to connect the chamber c with the suction area 612a and the suction couch roll 612 and/ or the suction boxes 615. Tracing the line 630, it will be noted that it is connected with a header 631 which is connected through a valve 632 to the couch roll suction area 612a and is connected through another valve 633 to the suction boxes `615. In operation, one of the valves 632 or 633 will be closed, of course, and as the vacuum increases in the line 630, the pressure decreases in the chamber c in the helper drive mechanism 624 and the tensioning roll 624]: is moved so as to tension the belt 624a. In other Words, as the load on the wire 611 is increased, as evidenced by increased vacuum in suction boxes and/ or the couch roll suction area 612, the helper drive mechanism 624 serves to increase the driving elect of the turning roll 616 to take up this load. The same type of helper drive arrangement is employed with each of the other smooth surfaced rolls, (not shown in FIG- URE The extent to which each of the rolls 616, 620 and 621 takes up driving load in response to changes in the vacuum may be altered by alterations of the piston sizes or the strength of the spring in the mechanism.

As has been explained hereinbefore, it is not believed that greater wear occurs on the wire 611 with increased normal pressures at the couch roll suction area 612a. The normal pressure ordinarily applied as a result solely of the tension in the wire 611 is in the neighborhood of l to 2 pounds per inch; whereas a rfull vacuum of perhaps inches of mercury on the relatively small effective area of the suction roll may result in a normal pressure of as much as 22 pounds per square inch. The helper drive mechanism 623 for the suction couch roll 612 is somewhat diiferent from the helper drive mechanism 624, because a different function is desired. First of all, the drive mechanism 623 comprises the usual slip belt 623m, plus the tensioning pulley 623b which is carried by a shaft 623e carrying pistons 623:1 and 623e and held in position by a packing gland 623f. A cylinder 623g receives the pistons 623d and 623e and defines with the rear piston 623e a small chamber c1 which communicates with the vacuum header 631. As will be appreciated, an increased vacuum in the header 631 results in a tendency to move the tensioning pulley 6231) away from the slip belt 623a and thus relax the amount of drive imparted to the couch roll 612. This is consistent with the present concept of diminishing the amount of drive irnpanted to the wire 611 by the couch roll 612 with increased vacuum (which results in an increased normal pressure between the wire 611 and the suction couch roll 612).

It is also desired to avoid having full helper drive force applied when there is no vacuum, so as to cause slippage between the couch roll 612 and the wire 611 during startup, so the application of helper drive force in the mechanism 623 is brought about by the application of a given amount of fluid pressure behind the front piston 623d in a chamber c2. Air under pressure through the pump P and the valve 634 is passed in the chamber c2 in order to provide the maximum desired amount of tensioning of the slip belt 623a by the tensioning pulley 623b. This is the amount of tensioning required during startup of the machine, after the initial application of vacuum. In fact, in order to avoid appreciable helper drive operation before any vacuum is applied, the valve l634 is connected to the header 631 by appropriate control mechanism 635 which will not open the valve 634 until initial vacuum is applied to the system. It will be appreciated that other devices such as pneumatic, hydraulic or electrical can be employed to accomplish the same purpose here. The principal concept here is that the general actuation of the couch roll 612 is that of decreasing the driving effect thereof as the load is increased on the machine, and particularly as the vacuum is increased at the suction area 612a.

This application is a combined continuation in part of application Serial Nos. 525,482; iiled August l, 1955; 525,483, filed August l, 1955; and 528,774, led August 16, 1955, all applications now abandoned.

It will be understood that modiications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

l. A method of handling a looped Fourdrinier type forming wire that comprises supporting and tensioning the wire on a suction couch roll, a breast roll and guide rolls, and frictionally engaging the wire with a plain-surfaced roll in wrapping relation therewith adjacent said suction couch roll and driving said wire thereby.

2. A method of driving a looped Fourdrinier type forming wire that comprises supporting and tensioning the wire on a suction couch roll, a breast roll and guide rolls, and frictionally engaging the wire with a plain-surfaced driven roll in wrapping relation therewith outside of the loop to drive the wire.

3. A method of driving a forming Wire of a Fourdrinier type paper machine having suction boxes receiving the wire thereover and a suction couch roll receiving the Wire therearound, a wire tension 1],l between the suction boxes and the couch roll of 20 to 100 pounds per inch and a wrap around x on the couch roll after the suction area of about 30 to 120, which comprises driving the couch roll and increasing the minimum tens-ion so as to obtain a wire tension 1 after the couch roll that is more than n. ga

wherein e is the base of the natural logarithm, y is the coefcient of friction and z is x in radians.

4. A method of driving a Fourdrinier type forming wire travelling forwardly over suction boxes and then over a suction couch roll, the difference in tension across the suction boxes being 10 to 60 pounds per inch, which comprises maintaining a tension in the wire after the suction couch roll of 20 to 40 pounds per inch.

5. A method of driving a Fourdrinier type forming wire travelling forwardly over suction boxes and then over a suction couch roll, the difference in tension across the suction boxes being 10 to 60 pounds per inch, which comprises maintaining a minimum tension in the wire of 20 to 40 pounds per inch.

6. A method of driving a Fourdrinier type forming wire travelling forwardly over suction boxes and then over a suction couch roll, the difference in tension across the suction boxes being l0 to 60 pounds per inch, which comprises frictionally engaging the wire with plain-surfaced driving rolls urged thereagainst at normal pressures in the range 1/2 to 8 pounds per square inch and driving the wire substantially entirely therewith.

7. A method of driving a Fourdrinier type forming wire travelling forwardly over suction boxes and then a suction couch roll, the wire tension ta after the suction box and before the couch roll being 20 to 100 pounds per inch and the Wire tension tb before said suction box being 10 to 50% ta, which comprises frictionally engaging the wire after the suction couch roll with a plain-surfaced roll :and driving the wire-therewith to lmaintain a tension drop across the couch roll of to 25% (ta-tb).

8. A method of handling a looped band that comprises engaging the inside of the loop of the band with a plurality of spaced perforate and imperforate surfaces, supporting and tensioning said looped band by urging said surfaces against the inside thereof, drawing a vacuum at said perforate surfaces to urge the band thereagainst, and engaging the band with a driven imperforate surface to move the band peripherally over the spaced surfaces inside the loop thereof, said band being decreased in tension over said driven surface 30% to 100% 0f the difference between the maximumiand the minimum tension in the travelling band and the normal pressure between the band and driven surface being not more than 3v pounds per square inch.

9. A method of driving a Fourdrinier type forming wire travelling forwardly over suction boxes and then over a suction couch roll, the difference .in tension across the `suction boxes being l0 to 60 pounds per inch, which comprises frictionally engaging the wire after the suction couch roll with a plain-surfaced roll and driving the Wire therewith to maintain a tension drop across the couch roll of 0 to 25% of said difference.

10. A method of handling a looped band that comprises engaging the inside of the loop of the band with a plurality of spaced perforate and imperforate surfaces, supporting and tensioning said looped band by urging said surfaces against the inside thereof, drawing a vacuum at said perforate surfaces to urge the band thereagainst, and engaging the band Lwith a driven imperforate surface to move the band peripherally over the spaced surfaces inside the loop thereof, said band being decreased in tension over said driven surface 30% to 100% of the difference between the maximum and the tension in the travelling band.

11. In a vFourdrinier type paper making machine, a looped forming wire, a perforate surfaced couch roll within the loop of said wire at one end thereof, a breast roll within the loop of said wire at the other end thereof, a plurality of plain-surfaced rolls frictionally engaging the wire, the sum of the areas of the wrapped surfaces of said plain-surfaced rolls totaling -at least 180, and drive means rotating said plain-surfaced rolls to drive the wire substantially entirely therewith.

12. In a Fourdrinier type paper making machine, a looped forming wire, a perforate surfaced couch roll within the loop of said wire at one end thereof, a breast roll within the loop of said wire at the other end thereof, a plurality of plain-surfaced rolls frictionally engaging the wire, the sum of the areas of the wrapped surfaces of said plain-surfaced rolls totaling at least 180 and at least 40 of each of said plain rolls is wrapped, and d-rive means rotating said plain-surfaced rolls to drive the wire substantially entirely therewith.

13. In a Fourdrinier type paper making machine, a looped forming wire, a perforate surfaced suction couch roll within the loop of said wire at one end thereof, a breast roll within the loop of said wire at the other end thereof, a plain-surfaced roll also within the loop of said wire at said end thereof and wrapped by said wire, and drive means rotating said plain-surfaced roll for driving the wire by means of said plain-surfaced roll.

14. In a Fourdrinier type paper making machine, a looped forming wire, a perforate surfaced suction couch roll within the loop of said wire at one end thereof, a plain-surfaced turning roll also within the loop of said wire at said end thereof and wrapped by said wire, a breast roll within the loop of said wire at the other end thereof, and drive means rotating said plain-surfaced roll for driving the wire by means of said plain-surfaced roll.

15. In a Fourdrinier type paper making machine, a looped forming wire, a perforate surfaced couch roll within the loop of said wire at one end thereof, a breast roll within the loop of said wire at the other end thereof, a plurality of plain-surfaced rolls frictionally engaging the Wire, the sum of the areas of the Wrapped surfaces of said plain-surfaced rolls totaling at least the difference in tension across the suction boxes being l0 to 60 pounds per inch, a method of driving the forming wire which comprises frictionally engaging the Wire after the suction couch roll with the plain-surfaced rolls and driving the wire therewith to maintain a tension drop across the couch roll of 0 to 25% of said difference.

16. In a Fourdrinier type paper machine, a looped forming wire passing over suction boxes, the difference in tension across the suction boxes being 20 to 60 pounds per inch, a breast roll within the loop of said wire, ,a plurali-ty of plain-surfaced rolls frictionally engaging the wire, the sum of thewrapped surface of said plain-surfaced rolls totaling at least 180 and at least 40 of each of said rolls is wrapped, and drive means rotating said plain-surfaced rolls to drive the wire therewith such that the power input of the suction couch roll will result in less than 25% of the above said 20 to 60 pounds per inch total required to drive the forming wire.

17. In a Fourdrinier type paper making machine having a couch roll, a breast roll, a forming wire looped therearound providing a forming run and a return run, the improvement of at least one plain roll engaging the return run of the wire, means driving said plain roll, means Wrapping the return run around an appreciable portion of the plain roll and means maintaining the return run under tension, said wrap around and said tension cooperating to provide a driving lgrip between the plain roll and wire.

18. In a Fourdrimer type paper making machine, a looped forming wire, a plurality of rolls supporting said wire including a perforate surfaced suction couch roll Within the loop of said wire and a plain-surfaced roll engaging the wire and positioned outside the loop thereof, and drive means rotating said plain-surfaced roll for driving the wire through said plain-surfaced roll.

19. In a Fourdrinier type paper making machine, a looped forming wire, a plurality of rolls supporting said Wire including a perforate surfaced suction couch roll Within the loop of said wire and a plain-surfaced roll engaging the wire and positioned outside the loop thereof, drive means rotating said plain-surfaced roll for driving the wire through said plain-surfaced roll, and a helper drive between said drive means and said suction couch roll.

20. In a IFourdrinier type paper making machine, a looped forming wire, a perforate surfaced suction couch roll at one end of the loop, a breast roll at the other end of the loop, suction boxes intermediate the couch and breast rolls engaging the wire, a plain-surfaced roll outside of the loop engaging the wire, and means driving said plain-surfaced roll to drive said wire.

2l. In a Fourdrinier type paper making machine, a looped forming wire, a plurality of rolls supporting said wire including a perforated surfaced suction couch roll within the loop of said wire and a plain-surfaced roll engaging the wire, means driving said plain-surfaced roll to drive said wire, a helper drive between said means and said couch roll, a suction box defining a first suction area with said wire, a gland in said couch roll defining a second suction area with said wire, and means responsive to the vacuum `at one of said suction areas in control of said helper drive.

22. In a Fourdrinier type paper making machine, a looped forming wire, a plurality of rolls supporting said wire including a perforated surfaced suction couch roll within the loop of said wire and a plain-surfaced roll engaging the wire, means driving said plain-surfaced roll to drive said wire, a helper drive between said means and said couch roll, a suction box defining a suction area with said wire, and means responsive to the vacuum at said suction area in control of said helper drive.

` 23. In a Fourdrinier type paper making machine, a looped forming Wire, a plurality of rolls supporting said wire including a perforated surfaced suction couch roll within the loop of said wire and a plain-surfaced roll engaging the wire, means driving said plain-surfaced roll to drive said wire, a helper drive between said means and said couch roll, a gland in said couch roll defining a suction area with said wire, and means responsive to the vacuum at said suction area in control of said helper drive.

24. In a Fourdrinier type paper making machine, a looped forming wire, a plurality of rolls supporting said wire including a perforated surfaced suction couch roll within the loop of said wire anda plurality of p1ain-surfaced rolls engaging the wire, means driving one said plain-surfaced roll to drive said wire, a primary helper drive between said means and said couch roll, a secondary helper drive between said means and another of said plainsurfaced rolls, a suction boX defining a rst suction area with said wire, a gland in said couch roll dening a second suction area with said wire, and independent control means for each of said helper drives, each of said control means being responsive to the vacuum at one of said suction areas.

25. In a Fourdrinier type paper making machine, a looped forming wire, a breast roll within the loop of the wire, a perforate suction couch roll within the loop of the wire and spaced from the breast roll to cooperate therewith for training the wire to provide an upper forming run, an imperforate roll frictionally engaging the lower run ofthe wire, guide rolls frictionally engaging the lower run of the wire, main drive means rotating said imperio` rate roll to drive said wire, rst helper drive means interconnecting said imperforfate roll and said couch roll, second helper drive means interconnecting said imperforate roll and said guide rolls, a first suction area defined by suction boxes beneath the upper run of the wire, a second suction area dened by a suction gland in the couch roll, and pressure responsive control means for each of said rive means controlled by the degree of vacuum at one of said suction areas for automatically varying the driving elcct of the drive means for each roll.

References Cited in the ile of this patent UNITED STATES PATENTS 1,5 82,323 Warren Api'. 27, 1926 1,623,526 Coffin Apr. 5, 1927 1,885,163 White Nov. 1, 1932 2,222,469 Youngchild NOV. 19, 1940 2,369,674 Hornbostel Feb. 20, 1945 2,392,150 Hornbostel et al Jan. 1, 1946 2,415,351 Hornbostel et al Feb. 4, 1947 2,445,416 Baker et al July 20, 1948 2,694,345 Hornbostel Nov. 16, 1954 OTHER REFERENCES Manufacture of Pulp and Paper, volume 5, section 1, page 86 (1929) published by McGraw-Hill Book Company, 370 Seventh Ave., New York, N.Y.

Manufacture of Pulp and Paper, volume 5, McGraw- Hill, 3rd edition (1939), pages 71-79. 

1. A METHOD OF HANDLING A LOOPED FOURDRINIER TYPE FORMING WIRE THAT COMPRISES SUPPORTING AND TENSIONING THE WIRE ON A SUCTION COUCH ROLL, A BREAST ROLL AND GUIDE ROLLS, AND FRICTIONALLY ENGAGING THE WIRE WITH A PLAIN-SURFACED ROLL IN WRAPPING RELATION THEREWITH ADJACENT SAID SUCTION COUCH ROLL AND DRIVING SAID WIRE THEREBY. 